3GPP TSG RAN WG1 Meeting #47 R1-063326
`Riga, Latvia, November 6 – 10, 2006
`
`Source:
`NTT DoCoMo, Fujitsu, Mitsubishi Electric, NEC, Sharp,
`Toshiba Corporation
`ACK/NACK Signal Structure in E-UTRA Downlink
`Title:
`Agenda Item: 6.12.2
`Document for: Discussion and Decision
`
`1. Introduction
`The attachment of the UE ID to the ACK/NACK bits is inefficient because the ACK/NACK signal has
`only one bit per UE. Therefore, this paper proposes a basic structure for the downlink ACK/NACK
`signal without carrying the UE ID.
`
`2. Mapping Scheme of Downlink ACK/NACK Signal
`The ACK/NACK signal consists basically of one bit per UE especially when MIMO channel
`transmission is not employed. However, if the destination is indicated by also sending the UE ID, the
`required number of bits per UE becomes significantly larger such as 17 assuming a 16-bit UE ID.
`Therefore, indicating the destination without signaling is desirable for efficient control signaling and
`improving the ACK/NACK bit error rate.
`
`The downlink ACK/NACK signals must be transmitted only to the UEs to which the uplink
`shared data channel is assigned at the previous transmission time interval (TTI). The UE is informed of
`the assignment of the uplink shared data channel using the downlink L1/L2 control channel (scheduling
`grant) in that TTI. Therefore, we propose predetermining a one-to-one relationship between the index
`of the downlink L1/L2 control channel (scheduling grant) for assignment of the uplink shared data
`channel and the index of radio resources (index of sub-carrier sets for FDM or code index for CDM)
`for the downlink ACK/NACK. By using this approach, the UE can find the ACK/NACK signal to be
`decoded without any additional side information as shown in Fig. 1.
`
`
`TTI t
`
`Node B
`
`Inform UE n of the
`uplink radio resources
`assignment using x-th
`L1/L2 control channel
`
`UE n
`Transmit uplink shared data
`channel using the radio
`resources assigned by the
`x-th downlink L1/L2 control
`channel
`
`Decoding of uplink shared data channel
`
`TTI t+α
`(α is the round
`trip delay)
`
`Transmit ACK/NACK to
`UE n using the x-th
`radio resources
`(x-th sub-carrier set or
`x-th code)
`
`UE n directory decodes
`ACK/NACK mapped to the
`x-th radio resources
`
`
`Figure 1 – Basic principle of proposed mapping scheme for downlink ACK/NACK signal
`
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`BlackBerry Exhibit 1006, pg. 1
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`3. Transmission, Coding and Multiplexing Methods of Multiple Downlink
`ACK/NACK Signals
`3.1. Transmission Scheme
`Our view is that distributed transmission should be applied to the downlink ACK/NACK signal in
`order to achieve simple decoding at the UE and a large frequency diversity effect (similar view in [1]).
`If the downlink ACK/NACK signal is transmitted using localized transmission using the scheduled
`resource block (RB) with good channel condition for the destination UE, the received quality of the
`ACK/NACK signal is better than that for distributed transmission. However, the UE must detect the
`RB where ACK/NACK is mapped with blind detection. Therefore, pre-determined, i.e., non-scheduled,
`distributed transmission or localized transmission with frequency hopping is an appropriate
`transmission scheme to obtain frequency diversity.
`
`3.2. Channel Coding Scheme
`Employing joint coding between multiple ACK/NACKs for different UEs is beneficial to increase the
`coding gain. Meanwhile, separate coding including repetition coding is advantageous to achieve a
`larger power control gain. Based on the simulation results in [2], our preference is to employ separate
`coding. It should be noted that only for separate coding, the proposed efficient ACK/NACK mapping
`scheme in Sec. 2 can be applied. However, the coding gain using joint coding is FFS.
`
`3.3. Multiplexing Scheme
`When we assume separate coding, we can consider FDM and CDM [3]. Between FDM and CDM, our
`preference is to apply CDM since by using CDM, the transmission power of all sub-carriers allocated
`to the L1/L2 control channel can be made constant even when individual transmission power control is
`used for multiple user equipments (UEs) [4]. This property is beneficial in reducing the dynamic range
`of the transmission power of each sub-carrier and randomizing the other-cell interference. However,
`the impact of orthogonality destruction in CDM in a fading channel should be verified. Alternatively,
`FDM with cell-specific frequency mapping for multiple UEs or a hybrid of CDM and FDM can be
`used for the same purpose of interference randomization [4].
`
`4. Conclusion
`A basic structure for the downlink ACK/NACK signal was proposed. The features of the proposed
`downlink ACK/NACK signal structure are as follows.
`• UE ID-less transmission based on the one-to-one relationship between the index of the
`downlink L1/L2 control channel for uplink radio resource assignment and the index of
`ACK/NACK radio resources
`Pre-decided distributed transmission or localized transmission with frequency hopping
`Separate coding between UEs
`•
`• CDM based multiplexing between UEs (FDM with cell-specific frequency mapping for
`multiple UEs or a hybrid of CDM and FDM are alternative candidates)
`
`•
`
`
`References
`[1] 3GPP, R1-062625, Motorola, “Downlink Acknowledgement and Group Transmit Indicator Channels”
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`BlackBerry Exhibit 1006, pg. 2
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`[2] 3GPP, R1-063322, NTT DoCoMo, Fujitsu, KDDI, Mitsubishi Electric, NEC, Toshiba Corporation,
`“Coding Scheme of L1/L2 Control Channel for E-UTRA Downlink”
`[3] 3GPP, R1-063325, NTT DoCoMo, “Basic Multiplexing Schemes of Multiple L1/L2 Control
`Information in E-UTRA Downlink”
`[4] 3GPP, R1-061668, NTT DoCoMo, “Fast Transmission Power Control in E-UTRA”
`
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`BlackBerry Exhibit 1006, pg. 3